Dolby Pro Logic II and DTS Neo:6 are simulated (matrixed) multi-channel formats, and don't come close to discrete multi-channel as far as channel separation and quality is concerned.
So "near perfect 5.1 output" would be out of the question.
Expanded on, 29July16:
It has to do with what matrixed audio is: There are only 2 channels and they are "mixed" in particular proportions and phase-shifts to create the other three channels. In Pro Logic II, as an example, you start with L (left) and R (right), and the other three channels are then mixed as follows:
C (center) is an even mix of L and R.
Rear-Left is mostly L phase-shifted +90 degrees, plus some R phase-shifted -90 degrees.
Rear-Right is mostly R phase-shifted -90 degrees, plus some L phase-shifted +90 degrees.
So you see, there can be nothing in the center or rear channels that is not already in the left and right channels. Matter of fact, the person creating the mix has almost no control on what the final mix will sound like. It's a pre-canned audio illusion to give the feeling of surround, using only two discrete channels. Think about it - If it was possible to master PL2 audio to sound more discreet, don't you think the studios would have used it that way?
Here is a good Wikipedia explanation on matrixed audio. Pro logic II is at the bottom: